1. Field of the Invention
The present invention relates to reducing the accumulation of sludge in tanker ships and in particular to recovering the fuel value from crude oil tanker bottoms.
2. Description of Related Art
A particular problem arises when transporting crude oil and petroleum products in tanker ships in which sludge accumulates on the bottom of the cargo tanks and often accumulates to significant depths. Heavy crude oil often can contain as much as 3 to 5% of the crude oil volume in globular form. When this crude oil is put into the cargo tanks of a tanker ship, the globular oil settles to the bottom of the tank. As successive loads of crude oil are transitioned through the tank, a thick layer of the settled globular oil accumulates in the bottom of the tank as a heavy sludge.
The accumulated tank bottoms decreases the usable volume of the tank and decreases the volume of delivered oil to the destination, resulting in an economic loss of cargo volume during transit from the loading port to the destination port.
A normal method of disposing of the tank bottoms is to flush the cargo tank with sea water, often under high pressure, and to discharge the resultant mixture overboard after the ship is in open ocean waters. This is an economic loss, for that volume of tank bottoms discharged is lost crude oil volume.
Periodically the ship is withdrawn from service and put into a shipyard for maintenance. At this time it is customary to remove remaining sludge in the cargo tanks to inspect and repair, if necessary, the walls of the tanks. The tank bottoms removed in this operation is usually incinerated or otherwise disposed of at a cost, with the complete loss of the economic value of the crude oil.
There is presently no effective method in use to process the crude oil tank bottoms in the tanker so that the economic value of the crude oil sludge is retained for discharge at the destination terminal.